The invention relates to arrangements for supporting a catalyst in the exhaust conduit of an internal combustion engine. More particularly, the invention relates to arrangements for supporting a catalyst in the exhaust conduit of a marine propulsion device.
The substrate of an engine exhaust catalyst can reach temperatures as high as 1,600.degree. F. while being enclosed in a housing that has a much lower temperature. It is necessary to mount the substrate within the housing in some flexible manner to accommodate the different thermal expansion of the substrate and the surrounding housing. In many automotive applications, this is accomplished by enclosing the substrate in a compressible, semi-resilient blanket of ceramic fibers or woven metal wire. This "soft" retention means not only accommodates differential expansion, but also helps to isolate the substrate from vibration and provides an insulating barrier to heat flow between the substrate and the housing.
However, under some relatively severe vibration conditions, there may be enough motion of the catalyst within the blanket to damage the blanket. The blanket may be pounded to the point that it breaks up and either falls out in pieces or is eroded away if exhaust gases are able to bypass the catalyst and flow through the blanket area.
The differential expansion between the substrate and the housing can be particularly severe in a marine application, such as in a stern drive engine, in which the catalyst must be water cooled to control the temperature in the engine compartment of the boat. In this kind of application, the catalyst may also have to be mounted directly on the engine, and the catalyst is thus exposed to more severe vibration than is a catalyst that is remotely mounted with a flexible connecting pipe.
Attention is directed to U.S. Ser. No. 782,427 (Attorney Docket No. 72012/0040), filed Oct. 25, 1991 and assigned to the assignee hereof, and to U.S. Ser. No. 822,972 (Attorney Docket No. 72012/0800), filed Jan. 21, 1992 and assigned to the assignee hereof.
Attention is also directed to the following United States and Foreign patents:
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